The invention generally relates to perforating flat uncured reinforced thermo setting plastic material and more specifically, to "B" staging the material at the opening surface and not effecting the curing of the remaining portions of the material.
U.S. Pat. No. 2,244,550 teaches the use of heated pins to perforate thermo-plastic material by causing the material to melt with pin penetration.
U.S. Pat. No. 3,440,117 teaches the use of sonic energy to cause thermo-plastic to melt for the purpose of embedding a plurality of pins in a thermo-plastic blank.
U.S. Pat. No. 3,719,736 teaches a method of perforating thermo-plastic film with heated pins and provides a reinforced buildup of material around the penetration.
Problems exist in the state of the art perforation of this type of material.
When uncured thermo setting plastic type materials are perforated prior to curing so that they can be cured in compound curve shapes or various different shapes other than planner configuration the resin tends to flow due to its viscosity and partially or completely fill the perforation.
When the perforations are made in partially cured or "B" staged thermo-setting material, it has been found that the material tends to fracture when subjected to strain inducing forces when perforated by various methods.
These and other differences were not successfully overcome until the emergence of the instant invention.